Embossed cell analyte sensor and methods of manufacture

ABSTRACT

An analyte measurement system is provided having sensors with embossed test chamber channels. In one embodiment, the sensors are elongate test strips for in vitro testing, each test strip having a substrate, at least one electrode, an embossed channel in the electrode, and lidding tape covering at least a portion of the embossed channel. Methods of manufacture are also disclosed for filling the sensor channels with reagent, and for trimming the ends of the sensors to eliminate the need for a calibration code during use of the sensors with a meter.

FIELD OF THE INVENTION

The present invention relates to medical devices for monitoring analytesin a living body, such as monitoring glucose levels in people withdiabetes. More particularly, the invention relates to an analyte sensorhaving an embossed sample chamber.

BACKGROUND OF THE INVENTION

People with diabetes typically measure their blood glucose level bylancing a finger tip or other body location to draw blood, applying theblood to a disposable test strip in a hand-held meter and allowing themeter and strip to perform an electrochemical test of the blood todetermine the current glucose concentration. Such in vitro tests aretypically conducted at least several times per day. Detaileddescriptions of such glucose monitoring systems and their use areprovided in U.S. Pat. No. 7,058,437, issued to TheraSense, Inc. on Jun.6, 2006, which is incorporated by reference herein in its entirety.

In addition to the examples provided in U.S. Pat. No. 7,058,437, therehave been numerous other approaches to test strip sensor construction inthe field of in vitro blood glucose monitoring. Two common methods aredescribed below.

In the first common method of test strip construction, a mesh,insulation and lidding tape arrangement is used. In this method, a baseelectrode is first formed on a substrate. A surfactant-coated mesh isthen adhered to the base electrode by an overprinted layer of insulationink. The ink is applied in a printed pattern. The open (non-printed)area of the pattern forms the sample cell and defines the working areaon the base electrode. A lidding tape is then adhered to the uppersurface of the insulation printing leaving sufficient openings for theair to escape as the strip fills with blood during use.

A disadvantage of this method is that print registration accuracy andink rheology limits the smallest size of cell that can be manufacturedrepeatably. In addition, three separate processing steps are required,and the mesh and insulation materials are relatively expensive.

In the second common method of test strip construction, a die-cut spacerand hydrophilic lidding tape are used. This method typically involveslaminating a die-cut spacer to a hydrophilic lidding tape. The liddingtape is in turn laminated to a base electrode on a substrate. In mostcases, the adhesive used at all of the interfaces is pressure sensitive.The thickness of the spacer and layers of adhesive, coupled with thetwo-dimensional area removed from the spacer, define the volume of thesample cell.

A disadvantage of this second method is that gumming problems are oftenencountered when cutting pressure sensitive adhesives. Test stripmanufacturing equipment is typically what gums up, but test strip portson a user's meter can also be disabled by fouling caused by theadhesives. Additionally, mechanical punches can only be scaled down to acertain size. Also, in this process registration is critical in allplanes, and the materials used are expensive.

Applying a reagent coating during the manufacture of test stripspresents a challenge in situations where pad printing is not suitable.This challenge has been solved in two different ways, slot coating andspraying, each of which is described in turn below.

Slot coating uses a slot die and reagent pump to dose material onto amoving web. The pump rates, web transport rates, reagent rheology andslot geometry are all critical factors in achieving the desired coating.This method can be an ideal way of applying low viscosity reagents in acontrolled manner at high speeds. However, it suffers from a number ofproblems. The first problem is that it is a continuous process andtherefore coats areas of the web that are not functionally required forthe assay. This not only is wasteful of reagent but also causesvariations in height on the sides of the sample chamber, creatingproblems when sealing the chamber. If the sample chamber is not wellsealed, the sample blood may leach away from the defined measurementarea and provide erroneous results. Finally, providing a uniform stripewith the slot coating method can be problematic with some liquids sincethicker bands of material are often found at the edges of the coatedstripe.

Spraying is another method of laying fine coatings of reagent ontomoving webs but also suffers from some disadvantages. In a reversal ofthe situation seen with slot coating, it is not uncommon for the centerof the stripe to be thicker than the edges. This helps with samplechamber sealing, but is also not uniform. Since spraying is also acontinuous process, it too is wasteful of reagent, and it is difficultto define areas accurately without masks.

Even with tight controls on strip manufacture, there typically isvariation across different strip lots. In order to maintain accuratetest results, some type of strip calibration is usually employed. Forexample, a representative sample of strips from each lot can be testedafter manufacture. A calibration code can be determined from the testingand this code can be provided with each strip in the associated lot,such as on a packaging label. Before use of each package of test strips,the code can be entered into the meter, thereby calibrating the meterwith the particular strips being used to provide accurate test results.However, this requires the user to perform an extra step. Furthermore,if the user neglects to enter a new calibration code for a new packageof strips or enters the code incorrectly, inaccurate test results may beobtained, potentially causing harm to the user. Some manufacturers haveresorted to providing a machine readable code on each strip or strippackaging that can be read directly by the meter during use. While thismay reduce errors, these systems are not foolproof and add cost to thetest strips and meters. Another method of reducing calibration issues isto supply a sub-set of test strip production, having a given calibrationcode, to a given customer base having meters that are already calibratedfor use with those particular test strips. The remainder of the teststrip production is labeled with calibration codes and supplied to adifferent customer base having meters requiring manual entry ofcalibration codes. This method is only effective for the portion ofcustomers that do not need to use the calibration codes. Furthermore,product supply problems can develop if the calibration distribution doesnot match the demand of both meter bases.

SUMMARY OF THE INVENTION

According to aspects of some embodiments of the present invention, an invitro analyte monitoring system may be constructed to operate with aminimum of analyte fluid. In one embodiment, a sensor may be formed bylocating at least one electrode on a substrate, providing an embossedchannel in the electrode, coating the channel with a reagent andcovering the channel with a hydrophilic lidding tape. An opening to thechannel may be provided at a distal end of the sensor so that when ananalyte is applied to the opening, it is drawn into the channel bysurface tension (i.e. wicking). A vent may be provided near an oppositeend of the channel so that when the analyte fills the channel, airpreviously filling the channel can be evacuated through the vent.Aspects of the present invention are well suited for use withamperometric, coulometric, potentiometric and other sensor types.

According to other aspects of the invention, the embossing process maybe performed either before or after the electrode(s) is applied to thesubstrate. In one embodiment, electrodes may be applied to anon-conducting substrate before a channel is embossed. For example, goldmay be sputtering onto the substrate with a mask to form multipleelectrodes separated by portions of the non-conducting substratesurface. Alternatively, an entire substrate surface may be sputteredwith portions later being etched away to form spaces between multipleelectrodes. In either case, a channel or channels may then be embossedinto the electrode on the flat substrate. An advantage to this approachof post-embossing is that flat surfaced substrate material withelectrodes formed thereon can be purchased from a large number ofsources and then later embossed. With this approach it may also beeasier to control the final dimensions of an embossed channel if theembossing step is one of the last steps to be performed before thesensor is assembled.

In another embodiment, a channel or channels may be embossed into asensor substrate before an electrode or electrodes are formed on thesubstrate. With this pre-embossing approach, a much thinner coat ofconductor can be used. This may be particularly advantageous when usingexpensive conductors such as gold. In addition, conductor materials thatare more brittle can be considered for use with the pre-embossingapproach.

According to other aspects of the invention, an embossing process usedmay be a rotary or a flat bed process. Various channel cross-sectionsmay be employed, such as rectangular and V-shaped. According to oneembodiment, embossed channels may have a semi-circular cross-section andmay have a depth of less than about 200 microns. More preferably, thechannels may be less than about 100 microns deep. Most preferably,channels may be less than about 50 microns deep. The active length ofthe test chamber channel may often be dictated by the layout of the teststrip. According to one embodiment, an embossed channel is aligned witha longitudinal axis of a test strip. Other orientations may also beused. In one embodiment, the active length of an embossed channel (i.e.the length containing electrodes and reagent) may be less than about 10mm. More preferably, the active length may be about 2 to 7 mm, and mostpreferably the length may be about 3 to 4 mm.

According to aspects of the present invention, the above geometries mayprovide sample chambers with highly repeatable volumes as well aselectrode surface areas from strip to strip, thereby increasingaccuracy. In a particular embodiment, sample chamber volumes may be lessthan about 200 nanoliters, more preferably may be less than about 50nanoliters, and most preferably may be less than about 20 nanoliters.

According to aspects of the invention, reagent may be applied to thesample chamber channel through the use of a needle and squeegee,although other methods such as slot coating or spraying may also beused. Test strips are preferably manufactured in rows with the teststrips attached side-by-side, and then singulated into individual teststrips, such as by slitting or cutting, as one of the last manufacturingsteps. In one embodiment, one or more rows may form a moving web duringmanufacture. Reagent may be pumped through a needle or needles onto themoving web and a squeegee used to spread the reagent and wipe the excessfrom the web. Alternatively, test strips may be formed in individualsheets before being singulated, and the needle(s) and squeegee(s) may bemoved relative to the sheets to apply and spread the reagent.

Needle and squeegee deposition may take advantage of the volume of achannel already having been defined by an embossing step. The channeland surrounding area may have reagent deposited by the needle dosingsystem, which is then spread by the squeegee. The squeegee may collectand remove reagent from the flat areas surrounding the channel whileleaving the channel fully filled. The wet reagent may then be dried toleave behind a thin film only in the channel. The final coat weight maytypically be governed by reagent viscosity, squeegee hardness, squeegeepressure and reagent dilution. The delivery rate of the needle dosingsystem may be either perfectly balanced to the usage rate or may be inexcess with a re-circulation or total loss system employed on thesqueegee.

According to other aspects of the present invention, a process fortrimming the ends of the test strips may be provided to calibrate thesensors. After patterning electrodes, embossing, reagent coating andhydrophilic lid lamination as described above, the sensors mayessentially be functional. At this stage, preferably before individualsensors are separated from each other, a representative sample ofsensors may be tested to ascertain at least one calibration parameter ofthe batch, such as a slope and/or intercept of a calibration curve.Through characterization at the design stage of the sensors, a range ofslopes and/or other calibration parameters expected of the design may befound and a lower value may be selected for product release. By trimmingthe working area on the remaining electrodes the slope may then beadjusted to match this lower product release value. This trimmingprocess can produce sensors that all have essentially the samecalibration slope, thereby eliminating the need to mark the sensors witha calibration code and require that the code be entered into the testmeter before use. The embossed test strip design embodiments describedabove are particularly well suited to such trimming due to their longchannel lengths in relation to their cross sectional areas, and the factthat sensor registration need not be performed in more than onedirection during the trimming process.

Various analytes may be monitored using aspects of the presentinvention. These analytes may include but are not limited to lactate,acetyl choline, amylase, bilirubin, cholesterol, chorionic gonadotropin,creatine kinase (e.g., CK-MB), creatine, DNA, fructosamine, glucose,glutamine, growth hormones, hematocrit, hemoglobin (e.g. HbA1c),hormones, ketones, lactate, oxygen, peroxide, prostate-specific antigen,prothrombin, RNA, thyroid stimulating hormone, and troponin, in samplesof body fluid. Meters may also be configured to determine theconcentration of drugs, such as, for example, antibiotics (e.g.,gentamicin, vancomycin, and the like), digitoxin, digoxin, drugs ofabuse, theophylline, warfarin and the like. Such analytes can bemonitored in blood, interstitial fluid, saliva, urine and other bodilyfluids.

BRIEF DESCRIPTION OF THE DRAWINGS

Each of the figures diagrammatically illustrates aspects of theinvention. Of these:

FIG. 1 is a plan view showing a test strip sensor in use with aglucometer.

FIG. 2 is an exploded perspective view showing components of anexemplary embodiment of a test strip sensor constructed according toaspects of the present invention;

FIG. 3 is a perspective view showing the components of FIG. 2 in anassembled configuration;

FIG. 4 is a perspective view showing an alternative embodiment sensor;

FIG. 5 is a side elevational view showing reagent being dispensed anddistributed on a series of sensors according to aspects of the presentinvention; and

FIG. 6 is a plan view depicting a trimming process according to aspectsof the present invention.

Variation of the invention from that shown in the figures iscontemplated.

DETAILED DESCRIPTION

The following description focuses on one variation of the presentinvention. The variation of the invention is to be taken as anon-limiting example. It is to be understood that the invention is notlimited to particular variation(s) set forth and may, of course, vary.Changes may be made to the invention described and equivalents may besubstituted (both presently known and future-developed) withoutdeparting from the true spirit and scope of the invention. In addition,modifications may be made to adapt a particular situation, material,composition of matter, process, process act(s) or step(s) to theobjective(s), spirit or scope of the present invention.

FIG. 1 shows a top view of an exemplary analyte system 10, a glucometersystem in this particular embodiment. System 10 includes a handheldmeter 12 and disposable test strip sensor 14. Test strip 14 can beinserted into and removed from test strip port 16 of meter 12 forphysical and electrical interconnection therewith. Meter 12 includes aliquid crystal display 18 for displaying information to the meter user,and buttons 20, 22 and 24 for receiving input from the user.

In general, to take a blood glucose measurement with meter 12, a userinserts a new test strip 14 into port 16 of meter 12. Either before orafter strip insertion into the meter, a user lances a fingertip or otherpart of the body (i.e. an alternate site) to draw a small drop of blood26 to the surface of the skin. The meter and strip are positioned overthe drop of blood 26 so that one of the sample chamber ends 28 istouching the drop of blood 26. While this particular example teaches theuse of a side-fill strip, it should be noted that an end-fill, top-fillor other type of test strip may be utilized, as will be later described.Moreover, the analyte testing need not use a test strip at all. Forinstance, a rotary test wheel having multiple sensors may be providedinstead of individual test strips. In the present example, surfacetension (wicking) automatically draws a small amount of blood 26 intothe sample chamber and an electrochemical test is automaticallyperformed by meter 12 to determine the glucose concentration in theblood 26. The glucose level 30 is then displayed on meter 12.

Referring to FIGS. 2 and 3, an exploded view of an exemplary test stripsensor 32 constructed according to aspects of the present invention isshown. In this embodiment, sensor 32 includes a substrate 34, a coverstrip 36 and lidding tape 38. A fill trigger electrode 40, a workingelectrode 42 and a reference electrode 44 can be patterned near a distalend 46 of substrate 34. Conductive electrodes 40, 42 and 44 may beseparated by portions of non-conductive substrate 34, and may be linkedby conductive traces to connector pads 48, 50 and 52, respectively.During use of test strip 32, connector pads 48, 50 and 52 each mayelectrically connect with associated connector contacts (not shown)within meter 12 shown in FIG. 1. Fewer, additional or differentelectrode types may be used. For example, fill electrode 40 may beomitted, and/or a second working electrode may be added to allow forhematocrit compensation.

In this embodiment, channel 54 is embossed into substrate 34 andtraverses each of the electrodes 40, 42 and 44. A reagent is added tochannel 54, an example of which is later described below. Lidding tape38 may be applied to substrate 34, such as with a pressure sensitiveadhesive to cover channel 54. Cover strip 36 may be added, such as witha pressure sensitive adhesive, mainly for aesthetic reasons and toprotect the conductive traces. The above steps create a functional teststrip, as shown in FIG. 3. Additional manufacturing steps may beperformed, as will be later described.

The above construction forms a sample test chamber, bounded on thebottom by channel 54 in substrate 34, and on the top by lidding tape 38.An open end 56 of the sample chamber, located at or near the distal end46 of test strip 32, allows sample fluid such as blood to enter thesample chamber. Lidding tape 38, its adhesive, and the materials formingsubstrate 34 and electrodes 40, 42 and 44 all are preferablyhydrophilic. This arrangement allows the sample chamber to automaticallyfill with sample fluid by surface tension (wicking) when opening 56 isplaced in contact with the fluid. Preferably, the dimensions andtolerances of channel 54 and lidding tape 38 are selected to ensure thatchannel 54 extends towards the proximal end 58 of strip 32 farther thanlidding tape 38 to create a vent 60. Vent 60 allows air displaced by thefilling fluid to easily escape the sample chamber without impeding fluidflow. A gap 62, as shown in FIG. 3, can be left between cover strip 36and lidding tape 38 to help ensure that vent 60 is not blocked. In analternative embodiment, cover strip 36 may be omitted altogether toreduce material and assembly costs and to keep vent 60 exposed. Inanother alternative embodiment, one of cover strip 36 and lidding tape38 may overlap the other. For example, cover strip 36 may overlaplidding tape 38 by about 1 mm. Since the edge of the lower layer beingoverlapped has some thickness which creates a step, the upper layer isunable to form a perfect seal against the step. This incomplete sealextends the vent laterally along the step out to each side of test strip32.

Embossed channel 54 may align with the longitudinal axis of strip 32 tocreate an end-fill strip, such as shown in FIG. 3. In an alternativeembodiment, the channel may be perpendicular to the strip axis. Anexample of such a side-fill arrangement is shown in FIG. 1, with onesample chamber end 28 serving to fill the chamber with fluid in thisembodiment, and the sample chamber end 28 on the opposite side of thestrip 14 serving to evacuate escaping air. Other configurations forembossed channel 54 may also be used. FIG. 4 illustrates a variation ofstrip 32 shown in FIG. 3. In this alternative embodiment, the liddingtape 38′ of strip 32′ is shortened so that it does not extend to the endof strip 38′. In this embodiment, portions of channel 54 and substrate34 are exposed to create a landing pad 64 for receiving blood or otheranalyte, thereby forming a top-fill strip. In use, a drop of blood 26can be placed on landing pad 64 adjacent to or on top of the outer edgeof lidding tape 38′, as shown in FIG. 4. Blood 26 is wicked into channel54 between lidding tape 38′ and substrate 34 and is tested as previouslydescribed. Such an arrangement may be advantageous in settings such ashospitals where an analyte sample may be applied to the test strip bypipette.

According to aspects of the present invention, channel 54 may beembossed before or after electrodes 40, 42 and 44 are patterned onsubstrate 34. When channel 54 is embossed after electrodes are patternedon substrate 34, materials and processes may be chosen to avoidexcessive damage to the electrodes, such as straining the electrodematerial(s) so much that their resistances increase drastically or thematerials actually break. Such problems may be avoided by using aductile electrode material like gold or similar metals, and/or byincreasing the thickness of the electrode material(s). Male and femaleembossing tools may also be designed to reduce excessive material flow,thereby alleviating the above problems. A thicker and/or softersubstrate and a shallower channel are other factors that can lessen thedamage to the electrodes. By adjusting the tools, materials, thicknessesand processes used for making channel 54, an acceptable balance betweenchannel depth and electrode damage can be struck for a particular set ofsensor requirements.

A preferred substrate material may be PVC since it embosses readily.Another preferred material may be polyester. Polyester may not emboss asreadily as PVC, but its use may facilitate faster reagent drying times.Polyester may be heated to 75 degrees Celsius without shrinkage, whilePVC should not be heated above 55 degrees C. Polypropylene may beanother preferred substrate material since it offers a compromisebetween the properties of PVC and Polyester.

With the tools, methods and materials described above, a test strip 32having a very small sample volume and very repeatable geometric featuresmay be produced. The small sample volume allows users to perform“alternate site testing” (i.e. at locations other than the fingertips)and allows less blood to be drawn. This in turn reduces or eliminatesthe pain involved with drawing blood, may reduces the mess of bloodsamples on the skin and causes less trauma to the body. According toaspects of the present invention, sample sizes may be less than about 20nanoliters. Additionally, the repeatable geometric features that can beachieved by the test strips disclosed herein further increase theaccuracy and precision of analyte testing with the strips.

Referring now to FIG. 5, an exemplary arrangement for applying reagentduring the manufacture of test strips 32 is shown. In this embodimentshown, test strips 32 are formed side by side on a continuous web ofsubstrate material 34, to be singulated into individual strips 32 duringa later manufacturing process. Prior to the stage shown in FIG. 5,substrate 34 may be patterned with electrode material 44 and otherelectrodes (not shown), and channels 54 a-54 e may be embossed into theelectrodes and/or substrate 34, as previously described above. The webof substrate material 34 may then be moved in the direction of Arrow Ashown, under stationary reagent fill needle 66 and squeegee 68. Reagent70 may be pumped, gravity fed or otherwise supplied through needle 66onto moving substrate 34. Squeegee 68 can help spread reagent 40 acrosschannels 54 and wipe excess reagent from the electrodes and substrate34. Essentially all reagent 70 may be removed from the surface ofsubstrate 34, leaving reagent 70 only in channels 54, which are thenpreferably full. Reagent 70 may be precisely metered onto substrate 34to avoid wasting reagent 70. Alternatively, more reagent 70 than isneeded may be supplied to substrate 34 to ensure complete coverage, andthe excess may be recycled or discarded. FIG. 5 depicts a yet to befilled channel 54 a, a channel 54 b in the process of being filled withreagent 70 by needle 66 and leveled by squeegee 68, a channel 54 c thathas been filled and leveled, and two channels 54 d and 54 e that havebeen filled, leveled and now dried, leaving only a thin layer of reagent70 along the channels.

Depending on the configuration of substrate web 34 and/or otherparameters, single or multiple reagent needles 66 and/or single ormultiple squeegees 68 may be utilized. Multiple needles may provide thesame or different reagents to substrate 34. Needle(s) 66 need not have acircular or oval opening, but rather may have an elongated slot or adifferent shaped orifice. Squeegee(s) 68 need not be separate fromneedle(s) 66, but may be incorporated therein. The above arrangementsmay be utilized in batch processes rather than with the roll stockdepicted. For example, substrate cards (not shown) containing a finitearray of test strips 32 can be coated with reagent 70 and leveled byholding the cards stationary while moving needle(s) 66 and squeegee(s)68 (either separately or in tandem) over the test strip cards.

Referring now to FIG. 6, an exemplary embodiment is shown for trimmingtest strips 32 according to aspects of the present invention. After teststrips 32 are functional, a representative sample may be tested. Asufficient number of test strips should be tested (or in other words a“batch size” should be small enough) so that it may be safely assumedthat all test strips 32 in each particular batch if tested would yieldsubstantially the same test results as the representative sample. Basedon the test results, it may be determined that the entire batch hascertain calibration characteristics, such as having a calibration curvewith a particular slope. Rather than labeling the batch with thecalibration characteristic (e.g. slope) and calibrating a meter 12 tothe strip 32 during use, strip 32 may be modified during manufacture to“calibrate” it to the meter 12. By decreasing the volume of coveredchannel 54 and the area of the working electrode 44, the slope of astrip's calibration curve can be reduced to a preset value. To reducethe electrode area of an essentially finished test strip 32, arelatively small portion of the distal end 46 of the test strip 32 maybe removed. This can be accomplished by trimming a series ofunsingulated test strips 32 along line B, such as by slitting orcutting, as shown in FIG. 6. The location of cutting line B may bevaried depending on how much functional change to strips 32 is desired.A representative sample of the trimmed test strips 32 may again betested to ensure that each batch now has essentially the samecharacteristics. After trimming (if needed), test strips 32 may beseparated from each other. Alternatively, test strips 32 may besingulated first and then trimmed, if needed. The above-describedtesting and trimming procedures may be conducted before or after anyaging process. With use of the above manufacturing method, the need foruser calibration can be eliminated. Also, the corners of the distal ends46 of strips 32 may be chamfered to match the edges of workingelectrodes 44 shown in FIG. 6 to increase user comfort and ease of use.

As previously discussed above, a ductile electrode material may bechosen to avoid excessive damage to the electrode during an embossingstep. The following discussion is intended to provide definition to theterm “ductile”. The material response for ductile and brittle materialsare exhibited by both qualitative and quantitative differences in theirrespective stress-strain curves. Ductile materials withstand largestrains before rupture; brittle materials fracture at much lowerstrains. The yielding region for ductile materials often takes up themajority of the stress-strain curve, whereas for brittle materials it isnearly nonexistent. Brittle materials often have relatively largeYoung's moduli and ultimate stresses in comparison to ductile materials.

As for additional details pertinent to the present invention, materialsand manufacturing techniques may be employed as within the level ofthose with skill in the relevant art. The same may hold true withrespect to method-based aspects of the invention in terms of additionalacts commonly or logically employed. Also, it is contemplated that anyoptional feature of the inventive variations described may be set forthand claimed independently, or in combination with any one or more of thefeatures described herein. Likewise, reference to a singular item,includes the possibility that there are plural of the same itemspresent. More specifically, as used herein and in the appended claims,the singular forms “a,” “and,” “said,” and “the” include pluralreferents unless the context clearly dictates otherwise. It is furthernoted that the claims may be drafted to exclude any optional element. Assuch, this statement is intended to serve as antecedent basis for use ofsuch exclusive terminology as “solely,” “only” and the like inconnection with the recitation of claim elements, or use of a “negative”limitation. Unless defined otherwise herein, all technical andscientific terms used herein have the same meaning as commonlyunderstood by one of ordinary skill in the art to which this inventionbelongs. The breadth of the present invention is not to be limited bythe subject specification, but rather only by the plain meaning of theclaim terms employed.

1. A blood glucose sensor comprising: a substrate; an electrode formedon the substrate, the electrode including an embossed channel; and acover located over the embossed channel, whereby a sample chamber isformed between walls of the embossed channel and the cover, and whereinthe sample chamber is configured to receive a liquid analyte in vitroand wherein said sensor determines blood glucose concentration.
 2. Theblood glucose sensor of claim 1, wherein the substrate has alongitudinal axis and wherein the embossed channel is substantiallyparallel with the axis.
 3. The blood glucose sensor of claim 1, whereinthe substrate has a longitudinal axis and wherein the embossed channelis substantially perpendicular with the axis.
 4. The blood glucosesensor of claim 1, wherein at least a portion of the electrode havingthe embossed channel comprises a ductile material.
 5. The blood glucosesensor of claim 4, wherein the ductile material is gold.
 6. The bloodglucose sensor of claim 1, wherein the sample chamber has a volume ofless than about 200 nl.
 7. The blood glucose sensor of claim 1, whereinthe embossed channel has a depth less than about 200 microns.
 8. Theblood glucose sensor of claim 1, wherein the embossed channel has anactive length less than about 10 mm.
 9. The blood glucose sensor ofclaim 1, wherein the electrode arrangement further includes a fulltrigger electrode, and the embossed channel extends from a workingelectrode and a reference electrode to the trigger electrode.
 10. Theblood glucose sensor of claim 1, wherein the channel has a semi-circularshape.
 11. The blood glucose sensor of claim 1, wherein the channel isV-shaped.
 12. The blood glucose sensor of claim 1, wherein the samplechamber has a volume of less than about 50 nl.
 13. The blood glucosesensor of claim 1, wherein the substrate comprises PVC.
 14. The bloodglucose sensor of claim 1, wherein the substrate comprises polyester.15. The blood glucose sensor of claim 1 further comprising an enzymeoverlying the electrode.
 16. A system comprising: (a) a handheld meterhaving a port; and (b) the blood glucose sensor of claim 1 configuredfor insertion into the port.